The present invention relates to an extruded styrene resin foam and a method for its production. Particularly, the present invention relates to a board-like extruded styrene resin foam which is excellent in environmental compatibility, retains highly efficient thermal insulating property and has appropriate strength properties, and hence useful, especially, as a thermal insulation material, and to a method for the production thereof.
Hitherto, extruded styrene resin foams have been widely used as thermal insulation materials for buildings because of their desirable workability and thermal insulation characteristic. Many prior patents proposed techniques which use flons typified by flon 12, flon 142b and flon 134a in order to impart excellent thermal insulation characteristic to styrene resin extruded foams, in combination with halogenated hydrocarbons which are easy to permeate through styrene resin, typified by methyl chloride and ethyl chloride in order to achieve desirable mechanical properties, thermal stability of foams and productivity. These techniques have been widely adopted as general production methods and have become common.
On the other hand, in recent years, attention has been given to the ozone layer problem and the global warming problem. From such a viewpoint, the use of flon 134a, which is suitable for protection of the ozone layer, is proposed. However, there is further demand for selection of preferable blowing agent in view of a greenhouse effect. In addition, methyl chloride, ethyl chloride and the like are believed to be preferable to be replaced if possible from the viewpoint of environmental sanitation.
JP, A, 53-2564 has proposed a thick styrene resin extruded foam board having a density of 30 to 40 kg/m3 and an average cell size of less than 0.3 mm which can maintain good thermal insulation property semipermanently by adjusting a partial pressure of propane, butane or the like in cells to from 0.25 to 0.75 atm. However, as is apparent from the description or examples in the specification, there are restrictions such as the need of using methyl chloride together in order to produce the foam board in good productivity and the limitation of the foam density to a higher range in view of thermal insulation property.
The use of hydrocarbons containing no chlorine atom in molecule, ethers or inorganic gases such as carbon dioxide as a blowing agent has also been proposed.
On the other hand, JP, A, 7-507087 has disclosed a technique which uses dimethyl ether and carbon dioxide in combination in a specific proportion as a technique for providing a styrene resin extruded foam board having a thickness of 20 mm or more and a cross-sectional area of 50 cm2 or more.
This patent gives attention to that when dimethyl ether, which is expected to have ability to form cells by diffusing through cell membranes, namely, cell-forming ability, is used as a blowing agent, a thick foam body can be obtained. It, however, is natural that a foam board for a thermal insulation material is demanded to be sufficient not only in thickness but also in other physical properties such as thermal insulation property and strength at the same time from an industrial viewpoint. This patent, however, has never studied whether or not the foam can satisfy such demands for thermal insulation property and the like which are of industrial necessity. Thus the problem of providing useful foams which are produced industrially has not been solved.
The present inventors have proposed, in JP, A, 3-109445, a method to improve thermal insulation property of a foam not only by relying upon a slightly permeable blowing agent contained in cells but also by forming a cell structure in which smaller and larger cells are present together.
Furthermore, the inventors have also proposed, in JP, A, 7-278338, an improved method for forming such a cell structure in which smaller and larger cells are present together, the method being more suitable for industrial production.
In view of such prior art, an object of the present invention is to provide an extruded styrene resin foam prepared by using a blowing agent with environmental compatibility, the foam being extremely suitable for industrial production and having excellent thermal insulation property and mechanical properties, and to provide a method for the production of the foam.
That is, the present invention provides the following extruded styrene resin foams and methods for the production of the same.
(1) An extruded styrene resin foam obtainable by extruding and foaming a styrene resin using a blowing agent, wherein the blowing agent comprises mainly 40% by weight or more and 85% by weight or less, based on the whole amount of the blowing agent, of at least one ether selected from the group consisting of dimethyl ether, methyl ethyl ether and diethyl ether, and 15% by weight or more and 60% by weight or less, based on the whole amount of the blowing agent, of at least one saturated hydrocarbon selected from the group consisting of saturated hydrocarbons having 3 to 5 carbon atoms.
(2) The extruded styrene resin foam as set forth in the preceding paragraph (1), wherein a weight ratio of the ether to the whole blowing agent is 50% by weight or more and 85% by weight or less, and a weight ratio of the saturated hydrocarbon to the whole blowing agent is 15% by weight or more and 50% by weight or less.
(3) The extruded styrene resin foam as set forth in the preceding paragraph (1), wherein a weight ratio of the ether to the whole blowing agent is 50% by weight or more and less than 70% by weight, and a weight ratio of the saturated hydrocarbon to the whole blowing agent is more than 30% by weight and 50% by weight or less.
(4) The extruded styrene resin foam as set forth in any one of the preceding paragraphs (1) to (3), wherein a cell anisotropic ratio k, which is defined by the formula:
k=a/(axc3x97bxc3x97c)⅓
wherein, in sections of the foam, a (mm) is an average cell size in the thickness direction, b (mm) is an average cell size in the transverse direction and c (mm) is an average cell size in the longitudinal direction, satisfies the equation:
xe2x80x830.80xe2x89xa6kxe2x89xa61.25
and an average cell size, a, in the thickness direction satisfies the relationship:
ti 0.24xe2x89xa6axe2x89xa6xe2x88x921.1xc3x97k+1.62.
(5) A extruded styrene resin foam, which has a cell anisotropic ratio k, which is defined by the formula:
k=a/(axc3x97bxc3x97c)⅓
wherein, in sections of the foam, a (mm) is an average cell size in the thickness direction, b (mm) is an average cell size in the transverse direction and c (mm) is an average cell size in the longitudinal direction, satisfying the equation:
0.80xe2x89xa6kxe2x89xa61.25
and an average cell size, a, in the thickness direction satisfying the relationship:
ti 0.24xe2x89xa6axe2x89xa6xe2x88x921.1xc3x97k+1.62.
(6) The extruded styrene resin foam as set forth in the preceding paragraph (4) or (5), which has a density of 26 to 35 kg/m3.
(7) The extruded styrene resin foam as set forth in any one of the preceding paragraphs (1) to (6), wherein the cells constituting the foam comprise mainly smaller cells having a cell size of 0.25 mm or less and larger cells having a cell size of 0.3 to 1 mm, and the area of the smaller cells having a cell size of 0.25 mm or less accounts for 10 to 90% of a sectional area of the foam.
(8) The extruded styrene resin foam as set forth in any one of the preceding paragraphs (1) to (5) and (7), which has a density of 15 to 40 kg/m3.
(9) The extruded styrene resin foam as set forth in any one of the preceding paragraphs (1) to (8), which has a thermal conductivity of not more than 0.029 kcal/mxc2x7hrxc2x7xc2x0 C.
(10) A method for producing an extruded styrene resin foam comprising heat-melting and kneading a styrene resin, introducing a blowing agent into the styrene resin under pressure and conducting extrusion foaming, wherein the blowing agent comprises mainly 40% by weight or more and 85% by weight or less, based on the whole amount of the blowing agent, of at least one ether selected from the group consisting of dimethyl ether, methyl ethyl ether and diethyl ether, and 15% by weight or more and 60% by weight or less, based on the whole amount of the blowing agent, of at least one saturated hydrocarbon selected from the group consisting of saturated hydrocarbons having 3 to 5 carbon atoms.
(11) The method for producing an extruded styrene resin foam as set forth in the preceding paragraph (10), wherein a weight ratio of the ether to the whole blowing agent is 50% by weight or more and 85% by weight or less and a weight ratio of the saturated hydrocarbon to the whole blowing agent is 15% by weight or more and 50% by weight or less.
(12) The method for producing an extruded styrene resin foam as set forth in the preceding paragraph (10), wherein a weight ratio of the ether to the whole blowing agent is 50% by weight or more and less than 70% by weight and a weight ratio of the saturated hydrocarbon to the whole blowing agent is more than 30% by weight and 50% by weight or less.
(13) The method for producing an extruded styrene resin foam as set forth in any one of the preceding paragraphs (10) to (12), wherein the extruded styrene resin foam has a cell anisotropic ratio k, which is defined by the formula:
xe2x80x83k=a/(axc3x97bxc3x97c)⅓
wherein, in sections of the foam, a (mm) is an average cell size in the thickness direction, b (mm) is an average cell size in the transverse direction and c (mm) is an average cell size in the longitudinal direction, satisfying the equation:
0.80xe2x89xa6kxe2x89xa61.25
and an average cell size, a, in the thickness direction satisfying the relationship:
ti 0.24xe2x89xa6axe2x89xa6xe2x88x921.1xc3x97k+1.62.
(14) The method for producing an extruded styrene resin foam as set forth in the preceding paragraph (13), wherein the foam has a density of 26 to 35 kg/m3.
(15) The method for producing an extruded styrene resin foam as set forth in any one of the preceding paragraphs (10) to (14), wherein the cells constituting the foam comprise mainly smaller cells having a cell size of 0.25 mm or less and larger cells having a cell size of 0.3 to 1 mm, and the area of the smaller cells having a cell size of 0.25 mm or less accounts for 10 to 90% of a sectional area of the foam.
(16) The method for producing an extruded styrene resin foam as set forth in any one of the preceding paragraphs (10) to (13) and (15), wherein the foam has a density of 15 to 40 kg/m3.
(17) The method for producing an extruded styrene resin foam as set forth in any one of the preceding paragraphs (10) to (16), wherein the foam has a thermal conductivity of not more than 0.029 kcal/mxc2x7hrxc2x7xc2x0 C.
(18) The method for producing an extruded styrene resin foam as set forth in the preceding paragraph (15), wherein 0.05 to 2 parts by weight of at least one water-absorbing material selected from the group consisting of a water-absorbing high molecular compound, inorganic powder having many hydroxyl groups on its surface and silicate powder, and 0.2 to 1.5 parts by weight of water are made to exist in 100 parts by weight of the styrene resin when performing the extrusion foaming.